Engines are supplied with a mixture of air and fuel for combustion within the engine's cylinders that generates a mechanical power output. In order to maximize the power output generated by this combustion process, the engine is often equipped with a turbocharged air induction system. A turbocharged air induction system increases engine power by forcing more air into the cylinders than would otherwise be possible. This increased amount of air allows for enhanced fueling that further increases the power output generated by the engine.
In some multi-cylinder engines, exhaust pressure pulses generated by the different cylinders can negatively interact with each other and reduce performance of the associated turbocharger. In particular, when different cylinders of an engine fire out of phase with each other, high-pressure and high-temperature pulses of exhaust discharged from the cylinders can attenuate each other within a common manifold that feeds the turbocharger. When the exhaust pulses are attenuated, the turbocharger receives an exhaust flow with lower average pressures and temperatures. These lower pressures and temperatures impart less energy to the turbocharger.
Separate exhaust manifolds can be used together with a dual-volute turbocharger in some applications to help preserve exhaust pulse energy. The separate exhaust manifolds direct exhaust pulses from co-firing cylinders to separate volutes within the turbocharger. Doing so inhibits attenuation of the exhaust pulses, resulting in exhaust passing through the turbocharger at higher average pressures and temperatures. The higher pressures and temperatures impart more energy to the turbocharger.
An exemplary engine system having separate exhaust manifolds and a dual-volute turbocharger is disclosed in U.S. Pat. No. 3,383,092 that issued to Cazier on May 14, 1968 (“the '092 patent”). Specifically, the '092 patent discloses a six-cylinder engine having two separate exhaust manifolds connected between two groupings of co-firing cylinders and two separate volutes of a vaneless axial-flow turbocharger.
Although the system in the '092 patent may have improved performance due to conservation of exhaust pulse energy, it may still be less than optimal. Specifically, because the engine system of the '092 patent provides only single-stage turbocharging, it may be applicable to only low-boost applications. In addition, the axial flow turbocharger of the '092 patent may have low efficiency in particular applications where flow exiting the two volutes and entering corresponding vaneless passages of the turbocharger is poorly guided due to flow misalignment (high incidence) with blades of the turbine. Further, the engine system of the '092 patent may have poor exhaust emissions in diesel engine applications.
The disclosed engine system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.